Various types of knocking control systems for use with internal combustion engines are known and described in the literature, see, for example, German Patent Disclosure Documents DE-OS Nos. 26 59 239 (corresponding to U.S. Pat. No. 4,002,155); 28 01 512 (corresponding to U.S. Pat. No. 4,133,475); 30 09 046. They may cooperate with evaluation circuitry described, for example, in German Patent Disclosure Documents Nos. 29 18 420 and 30 10 324.
Engine knocking can be controlled in various ways, see, for example, "Automotive Handbook" issued by the assignee of the present application, Robert Bosch GmbH, first English edition 1976, chapter on knocking or pinging, page 246 et seq.
Knocking control systems are so arranged that they shift engine operating control parameters, for example ignition timing, with respect to a predetermined engine operation in such a direction that the engine operates just below the knocking limit thereof. This operation contributes to efficiency and decreased fuel consumption. Such systems, however, may include the danger that failure of a component therein, and particularly a component within the knocking evaluation or recognition system could shift the operating parameters of the engine towards knocking range, which may endanger the engine and lead to damage or possibly even failure thereof.